The Petoskey Stone is a fossilized coral, specifically the Hexagonaria percarinata coral. It was named after the city of Petoskey, Michigan, where it was first discovered.

Here's some more information:

* Found in: The Petoskey Stone is found in the Michigan bedrock, specifically in the Dundee Formation of the *Lower Silurian period*.

* Appearance: It has a distinctive hexagonal pattern, resembling a honeycomb. The coral's fossilized skeleton is made of calcium carbonate, which gives it a light brown to gray color.

* Popularity: The Petoskey Stone is the official state stone of Michigan and is a popular souvenir for visitors to the state.

* Other Locations: While it's most commonly found in Michigan, it can also be found in other areas of the Great Lakes region, including Ohio, Indiana, and Ontario, Canada.

If you're ever in Michigan, keep an eye out for these fascinating fossilized corals! They are a reminder of the ancient marine life that once thrived in the Great Lakes region.